This invention relates to a method of residual stress measurement by a semi-nondestructive dynamic technique in which damage to the object is so small that the object tested is not impaired for further service.
In the past, residual stress or internal stress measurements have been made using destructive techniques. All the measurement methods required the stress relief of a specimen, and this invariably meant that the specimen was cut up by hole drilling, electrical discharge machining (EDM), sand blasting, or trepanning. Hole drilling is the most common but has the undesirable feature that the drill works the surface locally and builds in its own stresses. The EDM method while good is awkward to implement in the field. Efforts to determine residual stress nondestructively have met with little success except for the use of x-rays, which are sensitive to surface distrubances. Moreover, x-rays penetrate only a few atom layers and this technique is not a bulk method.